1. Field of the Invention
The present invention relates to high frequency resonant cavity filters and, more particularly, to a technique for directly coupling multiple high frequency resonant cavity filters to a common port.
2. Description of the Prior Art
The use of a resonant cavity for high frequency filtering purposes is well known in the art. A resonant cavity housing generally contains a pair of coupling rods and a plurality of resonators. The size of such a housing generally depends upon the number of resonator rods within the housing that are required for a desired filtering characteristic. Often, as the number of resonator rods is increased to meet a narrow bandwidth resonant frequency requirement, the size of the resonant cavity housing will exceed a standard rack mounting dimension. It is therefore desirable to efficiently design the resonant cavity housing such that its physical size conforms to standard rack mounting dimensions.
It has been previously shown, in the U.S. Pat. No. 5,151,670, that it is also desirable to combine multiple high frequency filters into a single resonant cavity housing. A multiplexing resonant cavity housing allows multiple filters to use a common port, and thus the number of lossy external feedline cables is decreased. The Duplexing Filter combines two high frequency filters into one resonant cavity housing such that a common coupling rod, that is connected to an external port, is shared. The common coupling rod is positioned at the center of the cavity housing and a plurality of resonator rods are positioned outward from this center coupling rod position. Separate coupling rods for each filter are positioned at opposite ends of the cavity housing, such that each filter's resonator rods are positioned between their respective separate coupling rod and the common coupling rod. Again, however, as the number of resonator rods is increased to meet the higher selectivity requirements of the filter, the length size of the resonant cavity housing often exceeds the standard rack mounting dimensions.
The present invention maintains the benefit of allowing multiple high frequency resonant cavity filters to use a common port, while conforming the size of the multiple filter assembly to standard rack mounting dimensions.